Rare precious metals such as gold, silver, palladium and rhodium have been playing an increasingly important role in modern technology, and there has been a keen demand for wasteless and effective utilization and consumption of the precious metals.
In practice, however, various process liquids in precious metal plating processes, such as waste liquids of precious metal plating solutions, wash liquids and stripping solutions, which contain precious metal compounds, have not been so effectively utilized.
Where the precious metal is "gold", for instance, there is known a method of recovering gold from a gold-containing process liquid by electolyzing the liquid to deposit gold on a cathode (see Japanese Patent Application Laid-Open No. 55-164045 (1980)). According to the method, however, gold is recovered in the form of a metal (metallic gold), which needs to be converted through complicated and troublesome reprocessing into gold potassium cyanide or the like for reuse thereof in plating or the like.
There is also known a method of recovering gold contained in a process liquid by adsorbing gold onto an ion-exchange resin or activated carbon. In this method, however, it is not easy, after adsorption of gold on the ion-exchange resin or the like, to recover gold through dissolution thereof; therefore, the thus adsorbed gold has hitherto been recovered by incinerating the ion-exchange resin or the like. Accordingly, the method requires incineration of the expensive ion-exchange resin each time during recovery of the gold, leading to cost problems, and also has the problem that gold is recovered in its metallic form which cannot be easily reused, as in the above-mentioned method.